It has been conventionally known that a dip molded article for use in contact with the human body, such as a nipple, sin air ball, a glove, a balloon and a sack, is obtained by dip molding of a latex composition containing a latex of natural rubber. A latex of natural rubber, however, contains a protein causing an allergy symptom in the human body, and thus may be problematic in terms of use in a dip molded article that is in direct contact with the mucous membrane or organs of a living body. Therefore, studies about use of not a latest of natural robber, but a latex of a synthetic rubber such as synthetic polyisoprene and/or a styrene-isoprene-styrene block copolymer have been increasingly made (Patent Document 1).
For example, Patent Document 1 discloses a composition for dip molding, containing a latex of synthetic polyisoprene and/or a styrene-isoprene-styrene block copolymer having a weight average molecular weight of 10,000 to 5,000,000, and a sulfur-based vulcanizing agent and a vulcanization accelerator. The composition for dip molding described in Patent Document 1, however, has the following problem: the mechanical stability of a latex used for obtaining this composition is not sufficient and thus the storage stability of the latex is low, and thus rubber particle aggregation easily occurs in a subsequent step and an additional step of removing an aggregate is required; and the following problem: the occurrence of an aggregate causes a reduction in production efficiency (see Patent Document 1). In particular, such problems are remarkably caused when the cis content is as relatively high as 90% by weight.